FIG. 1 is a diagram showing a hidden node problem occurring in a conventional WLAN system.
In the WLAN system, when a plurality of stations STA 111 and 112 in a same Basic Service Set (BSS) perform data transmission with respect to an access point (AP) 100 simultaneously, air-time collision inevitably occurs due to characteristics of a channel access scheme in view of collision avoidance, which is a hidden node problem.
In addition, even when stations located in different adjacent BSSs perform data transmission, an interference may also be generated as shown in FIG. 2, thereby reducing efficiency of data transmission originally desired. This is referred to as an overlapped BSS (OBSS) interference problem. FIG. 2 shows the OBSS interference problem occurring in the conventional WLAN system.
To relieve such problems, access chances of stations may be temporally distributed in every BSS to avoid collision on frequency resources. However, the foregoing expected object may also be achieved by spatially distributing channel access attempts using an AP with a sector antenna. Such a technology is called sectorization.
In general, the sector antenna includes a plurality of planar antennas and may control flickering of individual transmission antennas and reception antennas. A device functioning as the sector antenna may be implemented using a combination of multiple antennas and signal processing such as beam forming. The sectorization has not been used in the conventional WLAN nor even technically discussed, due to its operational inconvenience.
However, in case of institute of electrical and electronics engineers (IEEE) 802.11ah and IEEE 802.11af that use a sensor application, indoor/outdoor M2M, and extended range cellular offloading as a main application, coverage is increased up to about 1 km. Furthermore, as a number of stations managed by one BSS is increased up to several thousands to several tens of thousands, the hidden node problem and the OBSS interference problem become so serious that efficient data transmission cannot be performed at all. Accordingly, there is a demand for a technology of considerably reducing the problems by spatially dividing operation of stations through sectorization in the WLAN system.